Turbidimeters are widely used to test the effectiveness of water filtration systems. Governmental regulations require that such instruments provide highly accurate readings. Unfortunately, a considerable degree of effort and expense is typically required to maintain this accuracy. Present turbidimeters must employ an incandescent light source, which utilizes a spectrum of light broad enough to measure small particles. Incandescent light sources cannot be modulated and must remain on constantly. This often causes relatively rapid deterioration of the light source and inaccurate measurements. To compensate for this, as well as for other factors such as sensor deterioration, electronic drift, variations resulting from standard container glassware, and the accumulation of dirt and other impurities on the test sample cuvette, the turbidimeter must be cleaned and re-calibrated on a regular basis. This usually necessitates costly and inconvenient manual intervention, as well as equipment down-time.
Instruments have been developed that perform re-calibration internally through means of appropriate software. See my co-pending patent application Ser. No. 008,874, filed Jan. 22, 1993. However, such re-calibration still involves a considerable degree of human intervention with attendant inconvenience, delay and expense. The operator must manually remove the cuvette and add an appropriate calibration standard. This is a messy procedure that involves the handling and mixing of carcinogenic substances such as Formazin. Additionally, this procedure has the disadvantage of viewing the standard solution through different glassware which introduces further inaccuracies into the system. And periodically, the surface of the cuvette must be cleaned and worn lamps or sensors replaced. In my above-referenced application, I have provided for a readily replaceable light source for a turbidimeter. However, even this light source deteriorates over time and eventually may cause inaccurate measurements. To date, a convenient system is not known for automatically and continuously re-calibrating turbidimeters and similar instruments between periodic maintenance checks so that a consistent accuracy is maintained.